Radio antenna system



Nov. 13, 1956 J. H. MULLANEY 2,770,802

RADIO ANTENNA SYSTEM Filed Nov. 13, 1951 3 SheetsSheet l 15/71? H M ulianey,

INVENTOR;

ATTORNEY RADIO ANTENNA SYSTEM Filed Nov. 13, 1951 3 Sheets-Sheet 2 -]0]m H. Mullaney,

INVENTOR,

BY X/M? ATTORNEY Nov. 13, 1956 J. H. MULLANEY 2,770,802

RADIO ANTENNA SYSTEM Filed Nov. 13, 1951 3 Sheets-Sheet 3 John [1M zzllane y,

INVENTOR BY W @71 ATTORNEY RADIO ANTENNA SYSTEM John H. Mullaney, Washington, D. c., assignor to Dire caut Company, Washington, D. C., a partnership Application November 13, 1951, Serial No. 255,968'

6 Claims. (Cl. 343-852) This invention pertains to radio communication, and particularly to improvements in antenna coupling arrangements by means of which the di'rectivity of an antenna array can be controlled, while preserving proper impedance conditions between the array and a transmitter or receiver coupled thereto.

The invention is especially concerned with the achievement of maximum effectiveness of receiver installations, and will be disclosed principally in connection with such an application; however, certain of its principles are applicable as well to the transmission of radio energy, as will be understood by those skilled in this art.

The effective use of highly directional antenna systems requires that certain conditions be met with respect to the installation of the receiving equipment. Thus, for point-to-point communications, whether voice or telegraph, directional receiving antennas offer promise of an increase in the strength of the received signal, but useful gains cannot be obtained in this manner unless the receiver is operated in a relatively noise-quiet location. To this end, it is important that the receiver be relatively remote from other buildings and obstructions, and particularly that it be remote from electrical sources of noise. It is also important that areal ground system be employed, consisting usually of copper screen under the building housing the receiver, to which at least twenty radial (buried) ground conductors are securely bonded. All of the electrical equipment associated with the receiver must be bonded to this ground system.

Given an installation meeting the above conditions, and assuming that adequate maintenance of the receiving equipment is practiced, the ability of a receiver to discriminate against unwanted signals is not necessarily increased by further increases, in signal-to-noise ratio. Indeed, where discrimination can be effected as between the direction of arrival of the wanted and unwanted signals, some sacrifice in signal-to-noise ratio may even be tolerated because this is no longer the limiting factor in communication dependability.

The present art of directional receiving antennas usually dictates a fixed beam array, such as by the use of stacked elements, rhombics, Vs, curtains or the like. These antennas can further be classified as either broad-band or fixed frequency, and regardless of classification, they are almost always designed to have a more or less concentrated beam (in the reception sense) in one direction of azimuth, the energy received from directions outside this beam being suppressed to a greater or smaller degree. The fixed frequency antennas oifer the greatest power gain, while the power gain of the broad-band antennas depends upon their frequency of operation.

Obviously arrays of the above kind are limited, in that if the position of the interfering signal source changes, reorientation of the arrays is required. Since the physical installation is generally elaborate, such changes cannot be carried out rapidly or efiiciently. While a rotary beam antenna can be oriented rapidly, it generally has limited 'nite States Patent ability to operate at different frequencies, and its pattern shape also is invariable.

From the above discussion, it is apparent that good military communications, as well as other types of pointto-point communications, require a directional antenna which not only can discriminate against undesired signals in the sense of direction of arrival, but also which will provide the maximum effectiveness regardless of the frequency of the arriving signals carrier, within the design limits of the installation.

It is therefore a principal object of the invention to provide an antenna and matching system which will enable the effective directional discrimination to be adjusted in azimuth, without requiring any physical movements of the antenna elements themselves, and which will provide proper signal matching between the antenna and the receiver for all values of the carrier frequency amplitude.

A further object of the invention is to provide such a system in which the antenna elements themselves are quite simple and even conventional, whereby installation and erection are facilitated; this permits the rapid establishment of communication centers for various purposes, and especially, where military conditions must be met.

An additional object of the invention is to provide an antenna system comprising a simple, two-tower array,,and means for adjusting the relative phasing of the signals received at each tower or element, whereby the pattern of antenna-gain against azimuth can be simply controlled by an adjustment of therelative phase at which the separate received signals are combined.

Still another object of the invention is to provide a matching circuit adapted to receive the separate signals from the elements of the array and to combine them in the necessary time-phase relationshipto provide the desired directivity pattern, and in which only a single control is required for this selection. At the same time, proper adjustment for optimum operation on any desired frequency is provided by the adjustment of very simple controls. The two functions are thus independently adjusted, whereby operation is possible by relatively uninstructed personnel.

A further object of the invention is to provide a switching system, in connection with the phasing adjustment controls, which will facilitate the adjustment of the controls for frequency of the received carrier in response to signal received from a single one of the antenna elements, so that the initial frequency-adjustment can be carried out promptly, and the system then converted to operation as a directional system without loss of time or special technical knowledge.

The above and other objects and advantages of the invention, and a preferred manner of accomplishing the same, will best be understood from the following detailed specification of a preferred embodiment thereof, taken in connection with the appended drawings, in which:

Fig. l is a perspective view of the exterior elements of the system, comprising the antenna elements themselves as installed,

Fig. 2 is a schematic plan view of the array, showing the details of the ground system,

"Fig. 3 is a series :of graphical representations of some of the directional patterns obtainable with the particular two-tower array of Fig. 1,

Fig. 4 is a schematic diagram of the elements comprising the phasing and adjusting network feeding the antenna signals to the receiver, and

Fig. 5 is a diagram showing a modified portion of the Fig. 4 network for the same purpose.

Referring now particularly to Figs. 1 and 2 :of the drawings, there is shown a radio receiving station comprising a pair of straight vertical towers 1 and 2, each provided with a ground system comprising a plurality of buried radial conductors '3 and '4. As shown in Fig. 2, a heavy copper bonding strap 6 connects the two ground systems, and the signal conductor from each tower antenna is indicated at 7 and 8 respectively, these leading to a common equipment housing or shelter wherein is disposed the receiving equipment and the matching apparatus of this invention. The spacing and heights of the towers 1 and 2 will be discussed in detail hereinafter, and while so far the description has dealt with the use of two spaced apart towers, it will be understood that other forms of separate radiationreceiving elements can be employed.

It is, of course, well known that the directional pattern of a pair of spaced transmitting antennas can be varied effectively by altering the phase relationship of the signals applied to the separate radiators; such an arrangement is described, for example, on page 803 of Termans Radio Engineers Handbook published by McGraw-Hi-ll in 1943. However, the application of these principles to receiving installations in which frequent and rapid changes of directional patterns must be obtained, involves considerable complication, in that the ordinary operator, particularly of a field station whose location may change from time to time, is not able either to predict or control the receptivity pattern with any degree of cortainty.

The present invention provides a completely organized system utilizing antennas of the type shown in Fig. 1, and in which the control of the directional pattern is achieved with a minimum number of controls which are of a type such that no calculation is required to obtain the desired pattern. These controls are readily set and readjusted by unskilled operators, and ensure optimum performance for any given installation. To do this, of course, requires means for continuously varying the phase relationship between the two signals received from the antennas, and for combining the phase-adjusted signals in such a way that losses due to impedance mismatch, for example, are minimized.

Fig. 3 of the drawings represents certain of the patterns which are readily obtainable by control of the phasing of the signals from the two towers. In each figure, one of the principal (maximum) amplitudes has been indicated by the vector y, and the patterns clearly illustrate the effective azimuthal shift of this vector as the phase angle between the two signals from the respective towers is varied through the indicated angles. This azimuthal shift ranges through 180, and 'by suitable switching means to substitute the connections between the towers, the remainder of the angular adjustment to cover a full 360 can readily be obtained. The patterns indicated in Fig. 3 are obtained in the special case of a separation between the towers of 225 (that is, a distance equal to 225/360 times the wave length of the received carrier), but similar patterns are obtained for other and different arrangements. One possible embodiment of the antenna control and matching system in accordancewith the invention is indicated schematically in Fig. 4of the drawings.

The two coaxial antenna leads are designated and '12, and the phase shift is obtained by a pair of networks 28 and 30. Network 28 is an M-derived network comprising a pair of inductances 32, 33 and ganged shunt capacitors 34, 36 and 38. A padder capacitor 40 is shunted across capacitor 36 for initial and balancing adjustments. The network is a T network comprising the inductances 42, 43 and a shunt capacitor '44.

The M-derived network 28 provides phase shift which may range from zero up to 270 or more, and the T network 60 perm-its an additional phase shift adjustable up to the order, in practice, of 160, these shifts being accomplished, as shown, without requiring the use of adjustable inductances. The accomplishment of a total of 360 of phase shift between the signals is carried out by switching one of the networks from one antenna lead to the other, as will be described in detail below.

Four three-position switches SW1, SW2, SW8 and SW4 are provided, and are ganged for unicontrol as indicated. In the first position, indicated 'by a, switches SW1 and SW2 connect the antenna lead 10 to the M-derived network 28 and thence to the transformer 46 whose secondary is connected to the receiver, while switches SW2 and SW3 connect the T-network 30 between the antenna lead 12 and the other terminal of the primary winding of transformer 46, the center tap of this winding being grounded. A tunable powdered iron core slug for fre-' quency or resonating adjustment of this transformer is indicated at '47.

In position b, switch SW3 connects networks 28 and 3-0 in series, and switch SW4 connects these two in series with the antenna lead 10. At the same time, switches SW1 and SW2 connect antenna lead 12 directly to the low side of the primary of transformer 46. This shifting of T-network 30 from the lead 12 to the lead 10 accomplishes a lump phase change asbetween the signals carried by the two channels, so that now the ganged capacitors 34, 36 and 38 can introduce phase shift sufficient to cover the balance of the required 360 range. Thus, position a of the switches may be thought of as enabling the adjustable M-derived network 28 to introduce a phase, change in the range of (very approximately) zero to while position b permits covering the rangev of about 180 to 360.

The third (c) position of the ganged switches connects (by switch SW1 and switch SW2) the lead 12 alone to the transformer primary, for purposes of frequency adjustments in the receiver and the transformer, the lead 10 being disconnected at thi time by switch SW3.

While the arrangement shown requires the manipulation of a switch in addition. to the ganged capacitors to achieve the full 360 of phase change, it is clear that the mechanical dial or control for the ganged capacitors can easily be arranged to perform the switching function automatically. For example, the dial may have a pin at a selected point around its edge, said pin engaging the lever of a toggle switch which will thus be operatedrat the end of 180 of rotation of the shaft of the ganged capacitors. Continuous unicontrol over the entire range can thus be obtained.

Frequency tuning of the transformer 46 can be accomplished by adjustment of slug 47 and the capacitor 48 shunting its primary winding.

The arrangement so far described makes no provision for correcting or alleviating the unbalances in level resulting from the different attentuation in the phasing network in its various adjustments, but this maybe achieved by the modified arrangement shown in' Fig. 5. In this figure, transformer 46' has its primary shunted by a pair of capacitors 50, 52,'at least one of which is adjustable, and the common connection between the capacitors is connected to ground. Adjustment of capacitor 52 in' effect shift the center-point connection along the primary winding, and enables unbalances in the input signals due to losses in the two phasing channels to beequalized. Perfect balance of the signal amplitudes in these channels is not essential, so long as adequate attenuation of the signals to be rejected is obtained.

The coaxial leads 10 and 12 are shown as coupled into the phasing network by respective L or half-sections comprising inductance 54 and variable capacitor 56, and inductance 58 and variable capacitor 60. Adjustment of these input sections, by their respective capacitors, enables preliminary lineup of the antenna signals to accomplish the desired impedance match from the coaxial leads to the phasing networks. -Once these are adjusted, for a particular signal to be received (or discriminated against, where the undesired signal is close to the desired frequency signal), they are not disturbed during the opcitation or adjusting the phasing network.

An important feature of the invention is that it operates very satisfactorily without the necessity for any special coupling means at the bases of the antenna towers; however, such base coupling may of course be used, Without departing from the spirit of the invention. Also, while it is preferred to utilize lines 7 and 8 (Fig. 1) of equal length, for reasons of equalizing attenuation in these lines, they may be other than equal. The arrangement of Fig. 5 will permit compensating for inequalities in attenuation, or conventional means in one of the lines may be employed for the purpose.

While the graphical presentation of Fig. 3 emphasizes the directions of maximum sensitivity of the array, the directions occupied by the zero or minimum sensitivity points are also important, these being the so-called nulls. For the purpose of eliminating disturbance from a particular source, and especially at a frequency close to the frequency of the carrier desired to be received, the array can be adjusted so that a null is directed toward the interfering signal, which can thereby be attenuated as much as 50 decibels with reference to the strength of the interfering signal as received on a single tower antenna.

The invention has been described in connection with a representative arrangement which, operating in the frequency range from 12 to 17 megacycles per second, had

the following component values:

Condenser 48 mmf 11.2-381 Condensers 34, 38 mmf 100 Condenser 44 mmf 200 Condenser 36 mmf 12476 Condenser 40 -mmf 20-125 Inductances 32, 33, 42, 43 mH .65

Values for other frequency ranges are readily obtained by calculation.

It will be seen from the above. disclosure that I have provided a system by which directional orientation of an antenna system may be achieved, and varied through a complete circle of azimuth, by the operation of a single control means, and without any physical movement of the extremely simple antenna elements themselves. Properly designed, such a system Will cover a large range of frequencies with components having determined values, but Where the system is to be employed over different channels, plug-in units for the M and T networks, and for the other reactive components, may readily be designed as appropriate for the frequencies in such channels or bands. Conveniently, and especially for field or military use, all of the components required to be changed for operation on another band may be incorporated in a single integrated plug-in unit, as will be apparent to those familiar with this art.

While I have described in detail a preferred embodiment of my invention, I Wish it to be understood that various changes and modifications can be made without departing from the spirit of the invention as defined in the appended claims.

I claim:

1. In a radio wav receiving system, in combination, a single pair of receiving antennas spaced from one another in a horizontal direction, means comprising respective channels for deriving signals from said antennas over said respective channels, means for combining the derived signals for application to receiving equipment, means for individually matching the impedances of the antennas to said combining means, and an M-derived phase shifting circuit in one of said channels for continuously adjusting the relative phase relationship of the combined signals through a range of the order of at least degrees of phase relationship, while maintaining the effective output impedance of said phase shifting circuit substantially constant, whereby to vary the resultant directional pattern of sensitivity of said antennas and thereby to discriminate against undesired signals.

2. The invention in accordance with claim 1, in which said M-derived circuit includes a plurality of ganged adjustable condensers bridged on said first channel for continuous phase adjustment of signals in said channel.

3. The invention in accordance with claim 1, in which said combining means comprises an output transformer having a tapped primary and a secondary winding, means conducting signals derived from said antennas to respective end terminals of said primary winding, a pair of capacitors bridged across said primary Winding, and means for adjusting one of said capacitors.

4. The invention in accordance with claim 1, including a fixed phase shifting T-network, and means for switching the last named network selectively into the channel from either of said antennas.

5. The invention in accordance with claim 1, in which said combining means includes an output transformer, and means for connecting said first channel direct to the primary Winding of said transformer and for simultaneously interrupting said second channel.

6. A phase adjusting network for combining signals from a pair of antenna elements, in selected phase relationships ranging from zero to 360 degrees relative phase angle, comprising a pair of channels each having input and output terminals, a continuously adjustable M-derived phasing section, a fixed phase shifting section, and switch means for selectively connecting said sections in the same or different channels connecting corresponding input and output terminals.

References Cited in the file of this patent UNITED STATES PATENTS 2,198,604 Everitt Apr. 30, 1940 2,244,628 Kotowski June 3, 1941 2,286,839 Schelkunotf June 16, 1942 2,466,354 Bagnall Apr. 5, 1949 2,585,842 Richardson Feb. 12, 1952 

